The problem of controlling the flow of large volumes of gases which may carry considerable amounts of particulates, is especially pronounced in the dust-removal or dust-separation field in which valves may be used to selectively control the flow of the contaminated gas to a plurality of filter units and/or the flow of sparging or filter-cleaning gases and/or the flow of the cleaned gas.
The duct systems in which such valves are used are generally of large diameter so as to be capable of handling correspondingly large gas volumes and frequently the valves must be capable of sealing one or more ports or branches of the duct system against high pressure differentials produced by suction or pressurized gases.
Installations in which such valves may be used for a variety of industrial purposes, include metallurgical or chemical plants, power-generating plants, factories or other installations for ventilation purposes, and whenever exhaust gases carrying particulates are produced and in which the exhaust gases must ultimately, after cleaning, be discharged into the atmosphere.
It is known in such systems to provide disk valves for control of the gases, i.e. valves in which a port of the valve housing built into the duct system is formed with an annular seat which is engageable by a valve member of generally disk shape and movable toward and away from the seat, generally along the axis thereof and perpendicular to the plane of the disk, by a valve actuator, stem or spindle.
In German patent DE-PS No. 505,133, for example, there is described a disk valve having two valve plates mounted upon a common spindle and provided with right-hand and left-hand threads, respectively, so that rotation of the spindle in one sense will cause the two plates to bear against opposing seats of respective ports while rotation of the spindle in the opposite sense draws the plates against a partition which is horizontally disposed between them.
This system has the significant disadvantage that selective opening and closing of the two ports whose seats are juxtaposed with the respective valve plates, cannot be carried out. Such valves, therefore, are not capable of being used in multiport applications in which it may be desirable to connect one of the aforementioned ports to yet a further port or branched as is the case with many dust-removal duct systems.
For this purpose, especially with duct systems having a large throughput and hence large flow cross sections, for example, the valves of filter housings operable under pressure or under suction, disk valves can also be provided.
Such valves can be used to cut off one group of filter tubes or bags while the filter surfaces are cleaned and to bypass the contaminated dust to another set of filter surfaces, to connect the filters at their outlet sides selectively to a clean-gas duct, to control the flow of a sparging or cleaning gas to the filters, etc.
Valves of this type have valve plates which can engage one or the other of a pair of ports selectively and generally the valves plates are provided as membrane or domed members of a relatively thin material such as steel sheet so that elastic deformation of the valve plate members can ensure effective seating thereof.
However, such valves have problems when they are used in the aforedescribed way for selective blocking of ducts for the cleaning gas or for controlling the flow of the contaminated gas or the cleaned gas to and from a group of filter elements, because it is frequently necessary to completely cut off a filter chamber or zone to allow change or replacement of the filter surfaces.
The earlier valves were not suitable for this purpose.